Possible influence of sudden stratospheric warmings on the atmospheric environment in the Beijing–Tianjin–Hebei region

Abstract. Using European Centre for Medium-Range Weather Forecasts fifth-generation (ERA5) and second Modern-Era Retrospective analysis for Research and Applications (MERRA-2) reanalysis and surface meteorological observation data, this study explores the possible impact of sudden stratospheric warming (SSW) events on air quality in the

Beijing–Tianjin–Hebei (BTH) region. Major SSW events are divided into polar vortex displacement SSW and polar vortex split SSW. As the duration of split

SSW events is longer and the stratospheric signal pulses propagate further

downward than displacement SSWs, subseasonal variability of the atmospheric

particulates in the BTH is larger during split SSWs. The air particulate

concentration is light before the SSW onset due to the enhanced perturbation

in the troposphere associated with strengthened planetary waves. The air

particulate concentration around the SSW onset dates begins to rise due to

weakening of the tropospheric disturbance as the enhanced planetary waves

enter the stratosphere. In the decaying period of the SSW, the air

particulate concentration decreases as the stratospheric negative northern annular mode (NAM) signal propagates downward. Specifically, in the pre-SSW

period of displacement (split) SSW events, a wavenumber-1-like

(wavenumber-2-like) anomaly pattern is strengthened. The East Asian winter

monsoon intensifies as the East Asian trough is deepened, especially before the split SSW event onset, leading to a cleaning period. Around the SSW

onset period as the tropospheric perturbation diminishes and the East Asian

winter monsoon weakens, a surge of air particulate concentration is

observed. After the SSW onset, due to the downward propagation of the

stratospheric negative NAM signal, cold anomalies form in northeastern East Asia, especially for split SSWs, corresponding to a cleaning period in

the BHT region. The local meteorological conditions during the SSWs are also

discussed.